Magnetic material



Sept. 14, 1937. i J w, D W ET AL Re. 20,507

MAGNETIC MATERIAL Original Filed April 17. 1926 Reissued Sept. 14, 1937- John wemieusnmwuiaeu, N.J.,and BandallGilliaHinsdalamaasslgmto Western Electrlc Company, Incorporated,

York, N. 1., a corporation cl New York- New Original No. 1,869,643, dated May 15, use, Serial No. 102,729, All! 1'1, 1928.

Applicationfcrre- July 11,.ma, sci-in a 90,120

21 Claims. 7 (U1- I'IH 1) This invention relates .to magnetic materials and magnet cores, and more especially to magnet cores for loading coils for telephone circuits and their method of production.

The principal object of the invention is the production oi a magnetic element having low core losses and a relatively high permeability to enable a given inductance to be obtained from a minimum amount of material, and possessing to 10 a high degree those electrical and magnetic .characteristics which make it highly desirable in elec- Y trical signalling apparatus, particularly in loading, coils for telephone circuits.

Innocordance with one embodiment, the present invention contemplates the construction of magnet cores of an alloy including nickel and iron-in finely divided form, heat treated to have a higher inherent magnetic permeability and lower inherent hysteresis loss than iron, and com-' o 6 bined with a suitable insulating material. Morespecifically; the' invention contemplates the formation of the magnet cores of a nickel iron alloy in finely divided form in which the proportionsof its constituents are more than 25% of nickel 25 ,and the remainder principally iron, and in a form which has proven satisfactory the nickel content being approximately 'ma'y, oi the whole. -'I'he metal particles are treated with a solution of chromic acid in the presence of an alkali and 30 a filler whereby the alloy particles are individu-' ally insulated after which they are compressed into cores of the desired shape and size. The cores are heat treated at the optimum temperature for the particular alloy of which the cores 5 are constructed to stabilise the insulator and to give a high permeability and low hysteresis and eddy current losses.

- It is believed that .the invention will be clearly understood fromthe following detailed descripac tion of one embodiment thereof and the accomm8 drawing, in which 11g. 1 is a perspective-view ofa section of a 'loading coil core made in accordance with the present invention, and

as Fig. 2 shows a plurality of thesesections as j sembled to form a completed core.

' It will be understood, however, that this is 'merely illustrative and theinvention is not limited to the production of this form of core, but is 601 adapted to the production of cores for magnetic articlesoimanyforms. v

In carrying out the present invention the mag-- netic material is prepared in the following man- The magnetic material employed is preiE- bi-ably prepared from a nickel 1 .1 a oy com-- monly "referred to as permalloy", whiclris treated in a manner more fully described in the copending application of C. P. Beath and H. M.- E.

. Heinicke; Serial No. 101,179, filed April 10, 1926,

toreduce the alloyto afinelydivided form. Experience has proven that where low eddy current losses are desired it is essential that the par- "ticles be .of a small size and preferably of suchsize that alloftheparticleswillreadilypassthroughwhat is generally known as a one hundred and twenty meslr screen and-a large percentage pass through a two hundred mesh screen. According to one embodiment of the invention the alloy is prepared bymelting approximately 18% parts of nickel and'21% parts of iron in an oxidizing atmosphere and mining the resulting alloy into a mold. When according to the foregoing process the resulting alloy will be exceedingly brittle and is therefore particularly adapted to be reduced to -a finely divided or dust form 20 fromwhich the finished-cores are molded.

After the brittle ingots are obtained they are successively passed through progressively reducing hot rolls, which'form the alloy into fiat slabs approximately thick. By the hot rollins as process the size of the crystalline structure is reduced which since the disintegration of the material takes place mainly at the crystalboundarieaisessentialinordertohavea. satisfactory. yield of. dust.- The rolled slabs are broken into short pieces and'are then crushed in a law crusher, hammer mill or any other suitable type of apparatus in which a further reduction occurs. Thematerialafterbeingpassedthrough the jaw crusher is subsequently rolled in a ball as mill until it isreduced to afine dust. This dust is jsieved through a one-hundred-and-twcnty mesh sieve and any residue is remelted and the foregoing operation is again repeated to reduce the material to a'finely divided form. Prior to 40 the addition of the insulating material the finely divided particles of the nickel iron alloy are an-' nealed in a closed container at a temperature of approximately 150 C. to 980 0., atemperature of about 925 C. having proven to'be one which as "produces very satisfactory results. It is then necessary to again reduce the annealed alloy which isnow in-the form of a cake, to a finely divided mi-m'sitei which it is miied with the mmuiiwr. so

According to one form of the invention, the

. insulator'for the dust particles is prepared by mixingflwingredients in approximately the. fol lowing. proportions: 5% parts of chromic acid, 5 parts of mews parts of water glass conipcsed 50 total solids and containing approximatel.58.parts'of SiOato 1 part ofNaaQ. Sumcient water is added to-the ingredients to make a rather stirring to prevent caking and to insure a thorough coating ofthe individual dust particles, but it is not heated to such a degree of dryness that the chromic acid loses its adhesive properties.- The dried insulated dust particles are then in a form suitable for pressing into cores or rings ,which are preferably formed with a pressure'of approximately 200,000 pounds per square inch. A high pressure is used order to increase theirdensity. since it has been found that the permeability of the rings increases with increased density. Following this step in the process of constructing the cores and withthey are annealed at the optimum annealing temperature of approximately 500 C. and cooled. In order to make the cores chemically stable and to remove all soluble substances such as chromates the cores are boiled in water until a solution obtained by boiling a crushed test ringin water will show only a trace of soluble chromates when tested with silver nitrate. After this operationthecoresorringsaredriedata of approximately 100 C. A few test rings may be made of dust insulated in the above manner and their permeability measured. Should their permeability betoolow,.it may be increased by the addition of a predetermined quantitys'of uninsulated dust to the pressed into rings.

A plurality of rings thus formed are then stacked coaxially to form a core on which the usual toroidal winding is applied, the number of such rings used depending upon the existing electrical characteristics with which the loading .eoils are to be associated.

Although the permalloy particles have Lbeen described as being insulated with a solution of chromic acid, water glass and tale in definite proportions,

it is of course to be understood. that v the proportions of the diflerent ingredients may be varied without departing from the spirit and scope of the invention; Also chromic acid alone may be used v mechanical strength is not an essential characteristic of the finished cores. Then, too, acids than chrqmic, may be used with satisfactory results, among these being molybdic, tungstic, antimonous and phosphoric acids, and the water glass and tale may be likewise replaced with other alkalies, such as sodium hydroxide and sodium aluminate and fillers such as zinc oxide, aluminum oxide and barium oxide and still produce magnet cores which are satisfactory from both an electrical and magnetic standpoint.

By using an alloy of the proportions stated in the preceding paragraphs and by following the foregoing method of insulating the individual alloy particles and-compressing the particles into accompanied by constant in fm'mingtheringsin temperature insulated dust before itis of the telephone circuit- -chromic acid, 4% parts as the insulator in such cases where v treating the finely divided the alloy to a'finely the finally'divided particles, reducing the product wi h or less hysteresis-and eddy current losses'as cores constructed according to previously knownmethods. but with much less core What is claimed is: Y 1. As a new article 3. As a new article of manufacture, a magnetic nce obtained by heat treating finely divided particiu of a magnetic alloy of nickel and iron separated by an insulating material comprising chromic' acid, water glass, and a filler. 4. As anew article of manufacture, a heat .treated magnetic substance composed of the end products of a heat treated mixture of finely d1.-

' vided nickel-iron alloy particles, chromic acid, an

alkali. and talc.

5. As a new article of manufacture, a magnetic substance obtained by heat treating finely divided particles of a magnetic alloy of nickel and iron insulating material comprising chromic acid, water 6. As a new article of manufacture, a magnetic endproducts of aheat treated mixture of finely divided nickel-iron separated by an glass, and talc.

composed of the alloy particles and an insulating materia. compoundedof 5% parts chromic acid, 4% parts water glass, and 5 parts talc.

me and much less-coil volume, are available.

7. As a new article of manufacture, a magnetic 'ce composed of the end products of a.

heat treated mixture of finely divided particles ofa magnetic alloy composed of more than 25% nickel and the remainder principally iron, chromic jacid, water glass, and talc.

8. As a new article of manufacture, a magnetic ce composedof the end products of a treated mixture of finely divided particles of a magnetic alloy composed of more than. 25% nickel and the remainder principally iron with an insulating material compounded'of 5% parts water glass, and 5 parts talc.

9. 'Ihe method of which consists in coating particles of a magnetic material with an insulating material, consisting of chromic acid, an alkali and a filler, and forming amass of such insulated particles into a homogeneous solid. r

10. The method of making magnetic structures composed of an alloy.- which-consists in reducing the alloy to a finely divided form, heat particles, reducing the product so obtained to a finely divided form, coating the resulting product with an insulating material comprising chromic acid, and forming a mass ofsuch insula particles into a homogeneous structure. v

11. The method of making magnetic structures composed of an alloy, which consists in reducing divided form, heat treating and forming a. into a homogeneous 12. The method of making magnetic structures composed of an alloy, which-con sists in reducing divided form, heat treating the'alioy to a finely making magnetic structures, '50

the finely divided particles, reducing the product so obtained to a finely divided form, coating the resulting product with an insulating material comprising chromic acid, forming a mass of such insulated particles into a homogeneous structure, and heating the structure to a high temperature. v

13. The method of making magnetic structures composed of an alloy of more than 25% nickel and the remainder principally iron, which consists in reducing the alloy to a finely divided form,

heat treating the finely divided particles, reducing the product so obtained to a finely divided form, coating the resulting product with an insulating material comprising 5 /2 parts chromic acid, 4 /2 parts water glass and 5 parts talc, and

forming a mass of such insulated particles into a homogeneous structure.

14. The method of making magnetic structures composed of an alloy of more than 25% nickel and the remainder principally iron, which consists in reducing the alloy to a finely divided form, heat treating the finely divided particles, reducing the product so obtained to a finely divided form, coating the resulting product with an insulating material comprising 5 parts chromic acid, 4 /2 parts water glass and 5 parts talc, forming a mass of such insulated particles into a homogeneous structure, and heating the structure at a high temperature.

15. The method of producing a magnetic struc-'- ture, which consists in mixing magnetic dust with an insulating material, forming a mass of the insulated dust into a homogeneous solid, and subjecting said solid to a heat treatment at an optimum temperature determined by the point of minimum loss.

16. The method of producing a magnetic structure, which consists in mixing magnetic dust with an insulating material, forming a mass of the insulated dust into a homogeneous solid, and heating the solid to a temperature of approximately 500 C.

17. The method of producing a magnetic structure, which consists in mixing magneticdust with an insulating material, including an acid as an element, forming a mass of the insulated dust into a homogeneous solid, and heat treating the solid at an optimum temperature determined by the point of minimum loss.

18. The method of producing a magnetic structure, which consists in mixing nickel-iron particles with an insulating material, Iorming a mass of the insulated dust into a homogeneous solid,

' and subjecting said solid to a heat treatment at an optimum temperature determined by the point of minimum loss.

' 19. As a new article of manufacture, a magnetic substance obtained by heat treating particles of magnetic material separated by an insulating material consisting of chromic acid, an alkali, and a filler.

20. As a new article of manufacture, a magnetic substance produced by heat treating particles of magnetic material separated by an insulating material consisting of chromic acid, water glass, and talc.

21. As a new article of manufacture, the end products of intermingled particles of a. magnetic material, chromic acid, water glass and a filler compressed into a unitary structure and heat treated.

JOHN WENDELL ANDREWS. RANDALL GILLIS. 

